U.S. Pat. No. 3,995,623 discloses a multi-lumen flow-directed catheter suitable for use in diagnosing cardiovascular and pulmonary diseases. When the catheter is used for thermodilution measurements, a bolus of cold liquid is injected into the right atrium or superior vena cava (through port 30) and the resultant change in blood temperature is detected by a thermistor (represented by numeral 35) in the pulmonary artery, such change in blood temperature being representative of cardiac output. Three lumens are required by the patented construction to achieve such operation, one lumen conducting gas for balloon inflation, another conveying liquid for the injection of the cold bolus (or for right atrium pressure monitoring, blood sampling, or infusion of therapeutic media) and a third carrying the thermistor leads. One or more additional lumens would be provided where further capabilities are desired; thus, the patent discloses a fourth lumen (C) which extends completely through the catheter body for use in measuring pulmonary arterial pressures when the catheter is in place and the balloon is deflated, or pulmonary capillary wedge pressures when the balloon is inflated.
While the multiple function capability is an important objective, especially for heart catheterization where it is desirable to obtain as much diagnostic information as possible in a single catheterization procedure, such an objective has been achieved in the past either by increasing the size (outside diameter) of such a catheter or by reducing the cross section of each lumen and, hence, lowering the performance characteristics of the catheter. Not only must the lumens be made smaller, if their number is to be increased without altering the catheter's outside dimensions, but the necessity of providing septa between the lumens requires a further reduction in lumen size. Even when the partitions or septa which define the multiple lumens are made as thin as possible, their thickness still substantially reduces the space available for the several lumens within a catheter of any given size. At the same time, the outside dimensions of such a catheter, which must be capable of passing through the vascular system without injury to the patient, must be kept as small as possible. A 4 French catheter (approximately 0.053 inch O.D.) would therefore generally be considered more desirable than a larger 6 French (0.078 inch O.D.) catheter in terms of ease of manipulation and reduced risk of possible complications in use. Consequently, in order to achieve multiple functions in a cardiac catheter of optimum size, it has generally been considered necessary to compromise the performance capabilities of such a catheter.
Other patents disclosing multiple-lumen catheters are U.S. Pat. Nos. 3,746,003, 3,833,004, 3,710,781, 3,634,924, 3,152,592, 3,044,468, 3,050,066, and 2,845,930.